The present invention relates generally to the art of welding power supplies having high frequency arc starters and/or stabilizers. More specifically, it relates to a spark gap assembly used to produce a high frequency signal in a welding, cutting or induction heating power supply.
It is well known to superimpose a high frequency signal on an AC welding voltage to assist in arc starting and/or arc stabilization. This involves applying a high voltage, low current signal at a high frequency across the arc.
A high-frequency voltage signal can be used to initially ignite an AC or a DC welding arc. The main advantage of this technique is that arc ignition occurs when the welding electrode is brought near the workpiece. Actual contact between the electrode and the workpiece is not needed to start the arc when this technique is used.
A high frequency voltage signal can also be used to stabilize an AC welding arc. In the event of arc rectification (e.g. extinguishment), the high frequency signal provides a voltage sufficient to maintain or restart the arc. The high frequency voltage assures a re-ignition of the welding arc every time the AC welding voltage passes through a null, thereby stabilizing the arc. The high frequency overlay may be applied only upon start-up, continuously, or as needed. When applied as needed, arc rectification is sensed and, after rectification has existed for several cycles, the high frequency component is supplied.
A variety of devices have been developed to create the desired high frequency signal. For example, switches that provide momentary ignition pulses immediately after the AC welding voltage passes through a null point have been developed. These known devices typically use ignition condensers that discharge intermittently between the electrode and workpiece through a switch in the form of a spark gap.
A spark gap is created when two conductive spark gap points (xe2x80x9cpointsxe2x80x9d) are held a fixed distance apart from each other. The spark actually arcs between two conductive spark gap surfaces, one on each point. Spark gap surface, as used herein, means the conductive surface of the spark gap point between which a spark arcs. Spark gap, as used herein, means the gap located between the spark gap surfaces across which the spark arcs.
A spark gap point or just point, as used herein, includes the spark gap surface and the rest of the body to which the spark gap surface is a part. Points are typically cylindrical in shape having a flat spark gap surface at one end. The present invention is not limited to cylindrical shaped spark gap points or flat spark gap surfaces, however, and other shapes can be used.
The assembly that holds the spark gap points in their proper position and orientation is called a spark gap assembly. A spark gap assembly, in addition to the spark gap points, can include a one or two piece plastic or ceramic housing, clamping members, heat sinks, electrical leads, retaining screws and other fasteners which hold together or hold in place the various components that make up the spark gap assembly.
One prior art spark gap assembly in common use for continuous duty cycle applications is shown in FIG. 1. Prior art assembly 100 includes four points 101, 102, 103, 104 mounted in four extruded aluminum heat sinks 105, 106, 107, 108. The points are located in holes 109, 110, 111, 112 (spark gap receptacles) in the heat sinks and are axially aligned with each other in pairs. Two points are in axial alignment with each other when their longitudinal axes are substantially aligned with each other (e.g. substantially the same axis). For points having flat spark gap surfaces at right angles to the point""s longitudinal axis, this provides for a substantially uniform spark gap distance at all locations between the spark gap surfaces.
The points are secured in their respective spark gap receptacles using retaining screws 113, 114, 115, 116.
The retaining screws clamp the heat sinks together around the points. Retaining fastener (bolt, screw, studs, nuts, etc . . . ), as used herein, means a fastener that is used, directly or indirectly, to tightly secure a spark gap point in a spark gap receptacle.
A jumper wire 117 electrically connects one pair of points in series with the other pair of points. Jumper wire 117 is electrically connected to the points using two of the four retaining screws 113, 115. Likewise, each set of points is electrically wired to power supply circuitry (not shown) using the other two retaining screws 114, 116 which are also used to clamp heat sinks 106, 108 around points 102, 104.
Heat sinks 105, 106, 107, 108 are mounted on a square porcelain (ceramic) base 118. Each heat sink is secured to base 118 from below using a pair of metallic screws 119-122 (only one screw from each pair is shown in FIG. 1). These screws pass through mounting holes 123-126 in base 118. The screw heads are sunk into the bottom side of ceramic base 118 to help prevent shorting to the welding power supply chassis. Nonetheless, the prior art assembly is typically mounted in a power supply chassis with a layer of insulating paper placed between the bottom side 127 of porcelain base 118 and the power supply chassis. The insulating paper is used to further reduce the possibility of a short occurring between the spark gap assembly and the power supply chassis.
This prior art spark gap assembly suffers from several problems. First, this prior art assembly is typically mounted in the welding power supply with the points oriented in the vertical direction. As such, the bottom two spark gap points 101, 103 have a tendency to fall out when their retaining screws 113, 115 are loosened or removed. This can occur during routine maintenance. It can also occur as a result of either thermal cycling of the heat sinks or vibrations encountered during normal power supply usage. When a point falls out, it may be lost or it may come in contact with other electrical components inside of the power supply.
Another problem with this prior art assembly is that it cannot be completely assembled until it is installed in a welding power supply. This is because the electrical leads from the power supply are attached to assembly 100 using retaining screws 114, 116. These same screws are used to secure points 102, 104 in their receptacles. This means that the retaining screws holding two of the points in place cannot be adjusted and tightened until final installation in the welding power supply is completed.
Prior art spark gap assemblies, like the one described above, are used in continuous high frequency applications and have points that are completely surrounded by heat sinks. In other words, the receptacles are defined by the heat sinks. This type of arrangement hag been used in the past to dissipate the heat that is generated during continuous high frequency applications. The heat sinks are mounted to an insulating base. As a result of this mounting scheme, the points in this prior art assembly are prone to misalignment.
Misalignment can occur at the time of assembly, during initial power supply installation, or over time. Misalignment occurring at the time of assembly is due to assembly error (e.g. improper alignment of heat sinks 105, 106, 107, 108 during initial assembly of spark gap assembly 100). This misalignment can be the result of tolerances in in mounting holes 123-126.
Misalignment can also result from the torque that is applied to heat sinks 106, 108 when electrical power supply leads are attached to spark gap assembly 100 via retaining screws 114, 116. This torque can cause heat sinks 106, 108 to rotate. The problem is worsened by the fact that the top surface of porcelain base 118 is an inherently slippery surface and heat sinks 105, 106, 107, 108 are prone to slide on that surface. Misalignment over time results when heat sink mounting screws 119-122 become loosened due to thermal cycling of the heat sinks or vibrations of the power supply during normal use.
Finally, this assembly requires the use of extra insulation to prevent shorts from occurring. As previously mentioned, insulating paper is typically used between ceramic base 118 and the power supply chassis. This insulating paper is also typically wrapped up around the sides of assembly 100 to protect the electrically conductive heat sinks from coming in contact with other power supply components or the power supply chassis.
A second prior art spark gap assembly that utilizes a single pair of spark gap points includes a pair of heat sinks mounted opposite each other along a longitudinal axis. The heat sinks are brass blocks and are mounted to a plastic housing base from below using metallic screws. For each brass block, the plastic base includes a pair of short raised ledges running perpendicular to the longitudinal axis, one on each side of each brass block. These ledges help prevent rotation of the brass blocks on the plastic base.
Each brass block includes a hole (spark gap receptacle) drilled longitudinally through its center for mounting a spark gap point therein. Each spark gap point is secured in its receptacle using a retaining screw (e.g. set screw in this case) that comes in perpendicularly from the top of the brass block.
This prior art spark gap assembly suffers from many of the same problems as the previous prior art assembly. To begin with, this prior art assembly is typically mounted in a welding power supply with the longitudinal axis running vertically. Thus, the spark gap point at the bottom of the assembly is prone to falling out if the retaining screw holding it in place is loosened during disassembly or during normal operation. In addition, the bare metallic screw heads on the bottom side of the housing are susceptible to shorting out to the power supply chassis.
Accordingly, a spark gap assembly that overcomes the problems with the prior art assemblies is desirable. Such an assembly preferably retains its points when its retaining screws are loosened or removed, can be completely assembled and adjusted prior to installation in a power supply and has all of its electrically conductive components insulated from the power supply chassis. Such an assembly also preferably provides for simple alignment of the points. Preferably, no initial adjustments will be necessary and alignment will be maintained throughout the life of the unit.
According to a first aspect of the invention, a spark gap assembly for a welding power supply includes a first spark gap point, a second spark gap point, a housing base, a first base groove and a point stop. The first and second spark gap points define a first pair of spark gap points having a first spark gap there between. The first base groove is located on the housing base and is disposed to axially align the first and second spark gap points with each other. The first point stop is disposed to retain one of the first or second spark gap points in the spark gap assembly.
The first base groove is interrupted by an insulating channel disposed in the vicinity of the first spark gap in other embodiments. The first pair of spark gap points is located between a pair of insulating walls in another embodiment. The point stop is disposed on the housing base in yet another embodiment.
The spark gap assembly includes a first clamping member having a first complimentary groove in one embodiment. The first complimentary groove in combination with the first base groove define a first spark gap receptacle to hold the first spark gap point. The spark gap assembly includes a second clamping member having a second complimentary groove in an alternative embodiment. The second complimentary groove in combination with the first base groove define a second spark gap receptacle to hold the second spark gap point in this embodiment.
The first and second clamping members are one piece and the first and second complimentary grooves are a single groove interrupted by an insulating channel in another embodiment. The first and second clamping members are heat sinks in an alternative embodiment. The base includes a first pair of blind mounting holes disposed to mount the first clamping member in clamped relationship to the housing base and a second pair of blind mounting holes disposed to mount the second clamping member in clamped relationship to the housing base in yet another embodiment.
The spark gap assembly includes a third spark gap point, a fourth spark gap point, a second base groove and a second point stop in other embodiments. The third and fourth spark gap points define a second pair of spark gap points having a second spark gap there between. The second base groove is disposed on the housing base and axially aligns the third and fourth spark gap points with each other. The second point stop is disposed to retain one of the third or fourth spark gap points in the spark gap assembly in these embodiments.
The first base groove is interrupted by a first insulating channel disposed in the vicinity of the first spark gap and the second base groove is interrupted by a second insulating channel disposed in the vicinity of the second spark gap in alternative embodiments. In yet other embodiments, the first and second pair of spark gap points are located between a pair of insulating walls.
An insulating channel is disposed between the first and second base grooves in one embodiment. An insulating wall is located between the first and second pair of spark gap points in another embodiment. The first and second point stops are disposed on the housing base in yet another embodiment.
The spark gap assembly includes a third clamping member having a second complimentary groove in one embodiment. The third complimentary groove in combination with the second base groove define a third spark gap receptacle to hold the third spark gap point. The spark gap assembly includes a fourth clamping member having a fourth complimentary groove in another embodiment. The fourth complimentary groove in combination with the second base groove define a fourth spark gap receptacle to hold the fourth spark gap point in this embodiment.
The third and fourth clamping members are one piece and the third and fourth complimentary grooves are a single groove interrupted by an insulating channel in one embodiment. The third and fourth clamping members are heat sinks in an alternative embodiment.
According to a second aspect of the invention, a spark gap assembly for a welding power supply includes a first spark gap point, a second spark gap point, a housing base, a base groove, an insulating channel and a pair of insulating walls. The first and second spark gap points define a pair of spark gap points having a spark gap there between. The base groove is located on the housing base and is disposed to axially align the first and second spark gap points with each other. An insulating channel is disposed to interrupt the base groove in the vicinity of the spark gap. The pair of spark gap points are located between the pair of insulating walls.
According to a third aspect of the invention, a spark gap assembly includes a first spark gap point, a second spark gap point, a housing base, a first heat sink and a second heat sink. The first and second spark gap points define a pair of spark gap points having a spark gap there between. The housing base includes a base groove disposed to axially align the first and second spark gap points with each other. The first heat sink includes a first complimentary groove which in combination with the base groove define a first spark gap receptacle to hold the first spark gap point. Likewise, the second heat sink includes a second complimentary groove which in combination with the base groove define a second spark gap receptacle to hold the second spark gap point.